U.S. Pat. No. 5,796,214 issued to the present inventor, and co-pending application Ser. No. 09/139,311, filed on Aug. 25, 1998 by Louis R. Nerone and David J. Kachmarik, both assigned to the instant assignee, disclose various ballast circuits for a gas discharge lamp of the type using gate drive circuitry to regeneratively control a pair of serially connected, complementary conduction-type switches of a d.c.-to-a.c. converter. The gate drive circuitry as between the foregoing patent and application differ from each other in some respects, but each includes a coupling circuit including an inductor for coupling a feedback signal to the control nodes of the switches.
It would be desirable to provide a circuit for clamping the output voltage of the foregoing types of ballast circuits. This would prevent overheating of components of a typical output circuit, so as to eliminate blackening or smoking of a ballast housing when a lamp becomes broken, for instance. It also would reduce the peak voltages during lamp starting. Additionally, performance ratings of various components could be reduced, to achieve lower cost, without sacrificing reliability.
It would be desirable to provide a circuit for clamping output voltage that can be made at low cost.